Making a Mercury high thrust propeller perform in reverse.

Any details you care to add about rebuilds, problems solved, how to do etc,
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Making a Mercury high thrust propeller perform in reverse.

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Re: Making a Mercury high thrust propeller perform in revers

Post by MoodyBlue »

Greg,
You missed one important part, and that is to drill the final holes at an angle approaching that of the internal web on the propellor. This increased angle as opposed to your drill at right angles to the centre line, increases the venturi effect by a further 50%. Using your flat rear view of the prop you can see the angles used for the internal webbing.

If you look carefully at my original pictures you can see evidence of the angle required, and I stress again, drilling straight down at right angles is less effective than getting the hose to sit at an angle.

Well done though for taking the time to detail the proceedure.

Jeff (Moody Blue)
Inventor of this system.
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Re: Making a Mercury high thrust propeller perform in revers

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Re: Making a Mercury high thrust propeller perform in revers

Post by MoodyBlue »

Tips
Use a vice to hold the propellor at the desired angle.

The first smallers holes can be at right angles to the hub centre.

The last hole can be done by using the highest drill press speed, patience, and slow advancing of the drill bit.

Doing this allows the bit to act more like a router than a drill bit, and the slow advance stops the drill bit catching and gouging out excess metal.

Cheers
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Re: Making a Mercury high thrust propeller perform in revers

Post by Paul124AC »

Greg and Jeff, that is brilliant. I can see how it works, I had to check to see what the date was tho! :lol: A couple of Q's

* The prop used is not the sliding one is it, it's the lower pitch/larger diameter one? The sliding one is supposed to re-direct the exhaust in a similar fashion, but apparently isn't that great.

* Any feedback on the longevity of rubber and epoxy? My initial reaction was why didn't you use ally tube and weld it? I guess rubber is cheap, easy, and simple to replace.

* I'd use a 12mm hand reamer, this would give you an excellent de-burred hole and you'd be able to get a good controllable angle, and I was wondering wether just the relief hole at an angle would be enough, might try that first before adding the tubes. Better still we'll get Zeb to experiment, he loves that stuff. :lol:

POTY gentlemen, well done.
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Re: Making a Mercury high thrust propeller perform in revers

Post by MoodyBlue »

Paul,
I did try just angled holes first, but the effect, if any, was not noticeable.

I then tried rubber as it was on the bench to find out what is the best angle in two planes ie in relation to the centre line, and as Greg has done, added a little more twist.

The intent was always to refine it then fabricate and weld aluminium pieces in place. Issue there is keeping the heat away from the rubber shock hub while welding.

In the end the burrs work well in retaining the fuel hose with-out the need for adhesives.
Also they are easy to replace if one ever comes loose, as it's about 20 cents worth of tube carried in the tool box as spares.

The end result on the Mariner 8hp on the back of a Boomaroo 22, using the fuel hose in my original pics, was that it now reverses so hard that the tiller loads up and pulls out of your hand :oops:

The other issue is as per Gregs disclaimer. It takes a fair leap of faith to put drill holes in a perfectly good propellor :roll:

Cheers
Jeff
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Re: Making a Mercury high thrust propeller perform in revers

Post by INMA »

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Re: Making a Mercury high thrust propeller perform in revers

Post by INMA »

Quote Jeff "The other issue is as per Gregs disclaimer. It takes a fair leap of faith to put drill holes in a perfectly good propellor" My first one was a new out of the box propeller, my faith in Jeff's work was justified.

There was a lot less stress drilling the old propeller in the photos.
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Re: Making a Mercury high thrust propeller perform in revers

Post by Wanton »

Hi Guys,

I just caught on to this discussion. I am sure that the example given here by Greg will work on the Mercury OB that does not have the sliding prop shaft. My prop was modified by Jeff and as he says in the comments above the way he installed the venturi tubes is slightly angled. The angle in designed so that when the outboard in put is reverse the gases are actually captured by the tubes as their angle is slewed!! (not sure of this term) to suck the gases out. The opposite is true when the motor is in forward gear, ie. the water is sucked in and forces the gases away from the shaft quicker.

Most certainly the modification by Jeff on the prop did work very well. I am guessing the the mods by Greg will also work because with the modifications at least there are escape routes for the gases when the prop is in reverse and the water pressure is increased from behind. I am guessing that this effect is the same as that experienced if the 8 HP Mercury had a sliding propellor.

Like Greg I bought a 4 bladed Solas propellor and it works. However I feel that although I have excellent reversing capacity now, I have lost a bit of power when in forward. Greg and I are going to be discussing this in a few days, I hope.

In conclusion if you have a reversing problem this modification of Jeff's and Greg's really does work.

Below is a picture of Jeff's modifictions to my propeller

Image

Below is a video of my modified propellor working (please ignore my confused Forward/Reverse commentary, I get like that way when I get excited :? :shock: )

[youtube][/youtube]
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Re: Making a Mercury high thrust propeller perform in revers

Post by phum »

Hello all,
Very interesting, Is the original document by Moody Blue still available?
Peter
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Re: Making a Mercury high thrust propeller perform in revers

Post by MoodyBlue »

Peter,
I never had time to document this procedure. I did post some pics of the first one I did on a Mariner 8hp.
Greg (Inma) put the time and patience in to document the procedure.

Cheers

Jeff
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Re: Making a Mercury high thrust propeller perform in revers

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Re: Making a Mercury high thrust propeller perform in revers

Post by Mojo »

Thanks for documenting the process Greg, beautifully done and very helpful. Not sure if it has been raised, but have you considered doing a Cruising Helmsman article about it?

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Re: Making a Mercury high thrust propeller perform in revers

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Re: Making a Mercury high thrust propeller perform in revers

Post by Mojo »

I bought the hithrust prop from Greg and he kindly completed the exhaust modification for me. Prior to this I was using a low pitch prop on a new 5hp 2stroke. The boat is 8m long and all loaded up was 1600-1700kg. Wow, what a massive difference. The old prop in reverse was near useless. It would instantly suck it's own gas when put in reverse. The prop would get no traction at all as it was spinning in gas, not water. The modification changed all this, she now reverses nicely and has plenty of bite.

Performs well in forward, but I suspect this is more due to changing to hithrust blades rather then the modification. Can sit on 6.5-7kts boat speed, the old prop maxed out at 5kts.

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Re: Making a Mercury high thrust propeller perform in revers

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Re: Making a Mercury high thrust propeller perform in revers

Post by MoodyBlue »

As the inventor of this tube method, I think I'm WAY MORE clever than any "Yankee" Expert :oops: :oops:

Jeff


Maybe feedback from Nick on "Hot Chocolate" as that is the oldest mod that has now been running for over four years now, and to my knowledge has never lost or had to replace the pressed in hose parts.
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Re: Making a Mercury high thrust propeller perform in revers

Post by granty »

Hi Inma,
In reply to your request for other peoples outcomes on the prop mods.Last year after reading your post on how to do it ,I used my old prop to do the mods with .Engine is a Yamaha 8 hp with a 9 by 7 high thrust prop.Prior to the mods ,in reverse it was absolutely useless tried everything slow ahead,low revs ,high revs,it just cavitated as you would know very awkward when trying to dock.
Anyhow the good news is IT WORKS ,in fact its that good I,ve left the old prop on and will do the same to the newer prop this winter.
The holes were drilled at right angles to the hub,and the fuel hose epoxied in at an angle also the end angle cut.
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Re: Making a Mercury high thrust propeller perform in revers

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Re: Making a Mercury high thrust propeller perform in revers

Post by sailingpeter3 »

Tonight Inma (Greg) kindly made the same modification to the high thrust prop on my new Mariner 5hp 2 stroke. (Yes, fingers do get crossed while watching 3 big holes being drilled into a new prop. No need to worry, though: Greg carried out the job calmly and professionally.)

Given my hibernation in Melbourne's winter it will be a few weeks before I get out onto the water for a trial. Can't wait to back into a marina berth at 6 knots! :lol:

Thank you again, Greg, for doing the work and to Jeff for the original idea.

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Re: Making a Mercury high thrust propeller perform in revers

Post by zebedee »

sailingpeter3 wrote:(Yes, fingers do get crossed while watching 3 big holes being drilled into a new prop. No need to worry, though: Greg carried out the job calmly and professionally.)
Private message to Inma:
You've got them fooled!

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Re: Making a Mercury high thrust propeller perform in revers

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Re: Making a Mercury high thrust propeller perform in revers

Post by sailingpeter3 »

sailingpeter3 wrote:Given my hibernation in Melbourne's winter it will be a few weeks before I get out onto the water for a trial.
I've just come back from two weeks on Gippsland Lakes and put the outboard through its paces. In a nutshell, the modified prop works brilliantly in reverse: it bites immediately and speeds off as if in forward - something I've never experienced with any other outboard / prop combination. Forward performance remains as good as ever. It's a joy - and safety feature - knowing that when reverse is needed it will work quickly and very well.

Happy sailing.

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Re: Making a Mercury high thrust propeller perform in revers

Post by MoodyBlue »

INMA wrote:To anyone doing it themselves, I learnt a lesson on Peter's propeller. Even though we center punched the hole position before drilling the first hole, the drill drifted off as it went through the soft alloy and not down the curve but in the worst direction possible.

I'd like to know why but may never know, I dropped the first drill size to about a 2mm drill and the other two holes were fine. Drilling the soft alloy took care and going up to larger drills in smaller size increments made it easy. I cant explain why but this time the soft alloy did not machine as smoothly as past holes in propellers. The final holes were fine but I was a bit frustrated even with the drill press.
If the final drill size is 12-13 mm then the second last drill size should be 10 mm.

For the final 12-13 mm angled hole select the highest speed the press has. This will allow the drill bit to act more like a lathe on the soft metal.

I used the same method for the first Mercury propellor and for Wanton's propellor with out any issues.

PS: Thanks for the compliment on inventing the idea. In reality I'm happy if I've contibuted to another TSP member being safer and less stressed.

Jeff
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Re: Making a Mercury high thrust propeller perform in revers

Post by AZAmagnum »

Does anyone know the part numbers for the Mariner and Tohatsu equivalent to the 6 x 8 3/8 Merc High Thrust prop ? ?

Ive got a 5hp 2stroke mercury and I'm pretty sure its got the "standard" tinny prop which is made of plastic I think. I'd like something that works better in reverse too.

Come to think of it, Ive got two high thrust props to suit an 8hp motor, maybe suzuki ? ? I'll check them out and see if anyone wants them.

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